This invention relates to an improved pumping unit using a band-and-pulley lifting system rather than the common rocker-arm or walking-beam system. U.S. Pat. No. 4,916,959, issued on Apr. 17, 1990, to Gordon R. Lively, discloses a belt-and-pulley lifting system similar to the type that is the subject of this application, and is incorporated herein by reference.
Prior belt-and-pulley lifting systems, including the preferred form disclosed in U.S. Pat. No. 4,916,959, employ a flat belt that is coupled at one end to a counterweight assembly and at the other end to a polished rod assembly. The polished rod assembly is coupled, through the polished rod and a rod string, to the down-hole pump. The counterweight assembly is in turn coupled to a drive system that drives the belt over a roller pulley assembly located near the top of the derrick structure.
The type of belt-and-pulley system described above has the significant advantage of being able to lift great loads efficiently, thereby improving oil-well pumping operations. Specifically, the belt, and the associated counterweight and polished rod assemblies, each have the capacity to bear great loads. However, there was previously no equally strong means for fastening the respective ends of the belt to the counterweight and polished rod assemblies. The system shown in U.S. Pat. No. 4,916,959 employed a series of plates that riveted or otherwise fastened the ends of the belt to the counterweight and polished rod assemblies Such fasteners are much weaker than either the belt or the counterweight and polished rod assemblies and are not capable of bearing the significant weight or stress carried by the overall system. As a result, the use of fasteners of the type disclosed in the prior art caused many failures and severely limited the overall capacity of the system.
The need exists, therefore, for an improved pulley-lifting system that eliminates the need for weak-link fasteners between the belt, or band, and the end assemblies it carries, therefore increasing the overall capacity and efficiency of the system.